For those who did slip in - and were caught - the casinos bore the brunt of the punishment, with fines of thousands of dollars.

Now casinos are backing a measure that would change the penalties for underage gamblers with the hope of delivering a stronger deterrent for teenagers trying to enter casinos. The legislation pending before Gov. Jay Nixon actually would lower the first-time offense for youths who show fake identification at casinos to an infraction instead of a misdemeanor, but it would impose a mandatory -- instead of optional -- $500 fine.

"If you can be fined $500 and you're under age 21, in a lot of cases, that might be an incentive to think twice," said state Rep. Noel Shull, R-Kansas City, a former chairman of the Missouri Gaming Commission, which regulates casinos.

Like with most legislation, Nixon has not indicated whether he will sign or veto the underage gambling measure, which is part of a broader bill also dealing with child support payments and urban police departments. He has until mid-July to make a decision.

Missouri has barred people younger than 21 from the gambling floor since its first casinos opened in 1994.

Current law makes it a misdemeanor - punishable by a fine of up to $500 and a maximum of six months in jail - for casino patrons of any age to show a false identification. Repeat offenders can face a stiffer misdemeanor, punishable by up to a $1,000 fine and a year in jail.

The legislation would leave those same penalties in place for adults age 21 and older. But it would create a new classification of penalties for minors - making the first offense an infraction with a mandatory $500 fine and future offenses misdemeanors punishable by fines of up to $500 and a maximum jail time of six months.

Shull, who served on the Gaming Commission from 2005-2011, said many minors who try to get into casinos are simply turned away and never prosecuted for misdemeanor crimes. His hope is that prosecutors will be more likely to pursue an infraction charge with a mandatory $500 fine - and that minors thus will be less likely to try to slip into casinos.

Shull's proposal originated from the Missouri Gaming Association, an industry trade group that is well acquainted with the incentive nature of fines.

Since 1997, Missouri casinos have paid $1.66 million of fines related to underage patrons, according to figures provided to The Associated Press by the Missouri Gaming Commission. Those include a pair of $250,000 fines levied in the early days of Missouri's casino industry and a total of $75,000 of fines paid for six underage gambling cases so far in 2013.

Last year, Missouri's casino's caught or prevented about 845 minors from gaining access to the gambling floors, said Mike Winter, the executive director of the Missouri Gaming Association. If fewer minors are caught on the gambling floor, that should translate to fewer fines for casinos.

"Really this is about providing a better deterrent to those minors," Winters said.

Yet it remains to be seen which is a stronger deterrent - the current threat of a misdemeanor criminal record, or a mandatory $500 fine included in the legislation.

"Here's my concern: Really, if you lessen the consequence, you encourage the behavior," said Keith Spare, chairman of the Missouri Council on Problem Gambling Concerns.

Gambling addictions can begin as young as age 6 and tends to rise through the teenage years as youths start betting on sports or get into casinos, he said. Youths and seniors comprise some of the fastest growing demographics of problem gamblers, because they often are looking for something to relieve boredom, he said.

Rather than simply charging underage gamblers with an infraction, Spare said it would be more productive to require counseling or an evaluation to determine whether they have a problem with gambling.

Chris Colabello hit a two-run home run, R.A. Dickey threw seven shutout innings and the Toronto Blue Jays beat the Kansas City Royals 5-2 in testy matchup Sunday, taking three of four from the AL's top team.